package summer_vacation.lvchang.myyVacation;

/**
 * Created by Administrator on 2015/9/6.
 */
public class Text45 {
    public static void main(String[] args) {
        int a = 0;

        for(int i=1 ; i<=20 ; i++){
            int b = i;
            int j = i;
            while(j>1){
                b=b*(j-1);
                j--;
            }

            a = a + b;
        }
        System.out.println(a);
    }
}
